The present invention relates to a device for controlling the brightness of dashboard lights in a motor vehicle, in which an electro-optical transducer aligned in the direction of travel changes the light intensity of the dashboard lights, using the output signal, as a finction of the ambient brightness in front of the vehicle, and the output signal of the electro-optical transducer, which is weighted by an evaluation unit using predefined algorithms, being supplied to a control unit for influencing the brightness of the dashboard lights.
A device for controlling the brightness of dashboard lights is described in German Published Patent Application No. 32 45 299. In this case, a photodetector is used as an electro-optical transducer, which is joined to the windshield of the motor vehicle by a fiber-optic guide. In this manner, the photodetector detects the brightness of the ambient range in front of the motor vehicle. The output signal of the photodetector, which is weighted by a microprocessor using predefined algorithms, is supplied to a control unit for changing the brightness of the dashboard lights. The brightness of the ambient range in front of the motor vehicle is only approximately monitored by this device, meaning that the change in brightness of the dashboard lights is inadequate, especially when there are objects driving ahead or objects located in the ambient range.
A similar device having a phototransistor as an electro-optical transducer is described in German Published Patent Application No. 44 09 777. The analog output signal of the phototransistor is converted into a digital signal, and the characteristic curve of the phototransistor is compensated for by a processing device in such a manner, that a signal proportional to the ambient brightness is acquired for changing the brightness of the dashboard lights.
Japanese Laid-Open Patent No. 60 24 0545 describes a device for automatically switching the headlights of a vehicle on and off, when it drives into and out of a tunnel. In this case, the change in the brightness in front of the vehicle is monitored using an image-processing sensor, e.g. a CCD camera, and the change is used by an evaluation and control unit for switching the headlights.
A CCD camera for controlling the brightness of the dashboard lights is not suitable as an electro-optical transducer, since the CCD camera has a small dynamic range and does not allow an absolute determination of brightness. An absolute determination of brightness would only be attainable by aperture and illumination-time regulation, which, however, can never be exactly determined.